#include <bits/stdc++.h>using namespace std;const int N = 2e5 + 10;
const int M = N << 2;int n, cnt[27], a[N][27];
int tr[M][27], tag[M][27], pos[M][27];
int sum;
string str;void pushup(int op, int u)
{tr[u][op] = max(tr[u << 1][op], tr[u << 1 | 1][op]);if(tr[u << 1][op] >= tr[u << 1 | 1][op]) pos[u][op] = pos[u << 1][op];else pos[u][op] = pos[u << 1 | 1][op];
}void build(int op, int u, int l, int r)
{int mid = l + r >> 1;if(l == r){tr[u][op] = a[mid][op];pos[u][op] = mid;return;}build(op, u << 1, l, mid);build(op, u << 1 | 1, mid + 1, r);pushup(op, u);
}void modify(int op, int u, int L, int R, int c, int l, int r)
{if(L <= l && r <= R){tr[u][op] += c;tag[u][op] += c;return;}if(tag[u][op]){tag[u << 1][op] += tag[u][op];tr[u << 1][op] += tag[u][op];tag[u << 1 | 1][op] += tag[u][op];tr[u << 1 | 1][op] += tag[u][op];tag[u][op] = 0;}int mid = l + r >> 1;if(L <= mid) modify(op, u << 1, L, R, c, l, mid);if(R > mid) modify(op, u << 1 | 1, L, R, c, mid + 1, r);pushup(op, u);
}int ps;int qmax(int op, int u, int L, int R, int l, int r)
{if(L <= l && r <= R){ps = pos[u][op];return tr[u][op];}int mid = l + r >> 1;if(tag[u][op]){tag[u << 1][op] += tag[u][op];tr[u << 1][op] += tag[u][op];tag[u << 1 | 1][op] += tag[u][op];tr[u << 1 | 1][op] += tag[u][op];tag[u][op] = 0;}int ans = 0;if(R > mid) ans = max(ans, qmax(op, u << 1 | 1, L, R, mid + 1, r));if(L <= mid) ans = max(ans, qmax(op, u << 1, L, R, l, mid));return ans;
}void query()
{int ans = sum - n;int pt = 1;for(int i = 2 ; i <= 26 ; i ++ ){int max_ = qmax(i, 1, pt, n, 1, n);if(max_ <= 0) break;ans -= max_;pt = ps;}cout << ans << '\n';
}
int main()
{freopen("lock.in", "r", stdin);freopen("lock.out", "w", stdout);ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);int q, op;cin >> op >> q;cin >> str;n = str.size();str = ' ' + str;for (int i = n ; i >= 1 ; i -- ){cnt[str[i] - 'a' + 1]++;sum += str[i] - 'a' + 1;int nsum = 0;for (int j = 26 ; j >= 1 ; j -- ){nsum += cnt[j];a[i][j] = nsum - (n - i + 1 - nsum);}}for (int i = 1; i <= 26; i++) build(i, 1, 1, n);query();while (q--) {int k;char x;cin >> k >> x;sum -= str[k] - 'a' + 1;for (int i = 1; i <= str[k] - 'a' + 1; i++) modify(i, 1, 1, k, -1, 1, n);for (int i = str[k] - 'a' + 2; i <= 26; i++) modify(i, 1, 1, k, 1, 1, n);str[k] = x;sum += x - 'a' + 1;for (int i = 1; i <= x - 'a' + 1; i++) modify(i, 1, 1, k, 1, 1, n);for (int i = x - 'a' + 2; i <= 26; i++) modify(i, 1, 1, k, -1, 1, n);query();}return 0;
}
