#include<bits/stdc++.h>
using namespace std;
const int N = 300002;
int n, k, pre[N], dp[N];
struct node {
int num, id;
bool operator < (const node &t) const {
if(num == t.num)
return pre[id] < pre[t.id];
return num > t.num;
}
};
priority_queue <node> q;
int main() {
char ch;
scanf("%d %d", &n, &k);
scanf("\n");
for(int i = 1; i <= n; i ++) {
ch = getchar();
if(ch == 'G')
pre[i] = pre[i - 1] + 1;
else
pre[i] = pre[i - 1] - 1;
}
q.push((node) {0, 0});
for(int i = 1; i <= n; i ++) {
while(q.top().id < i - k)
q.pop();
dp[i] = (pre[i] >= pre[q.top().id]) ? q.top().num + 1 : q.top().num;
q.push((node) {dp[i], i});
}
printf("%d\n", dp[n]);
return 0;
}
