#include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <queue>

 #include <map>

 #include <ctime>

 #include <cmath>

 #include <algorithm>

 using namespace std;

 #define INF 1000000

 char str[];

 int dp[];

 int pre[];

 int que1[];

 int que2[];

 int judge(char s)

 {

     if(s <= 'Z'&&s >= 'A')

         return ;

     else if(s <= 'z'&&s >= 'a')

         return ;

     else if(s == ' ')

         return ;

     else

         return ;

 }

 int main()

 {

     int n,m,i,j,len,str1,end1,str2,end2;

     scanf("%d%d%*c",&n,&m);

     gets(str);

     len = strlen(str);

     for(i = ; i < len; i ++)

     {

         if(judge(str[i]))

         {

             for(j = i; j < len; j ++)

             {

                 if(judge(str[j]))

                 pre[j] = i;

                 else

                 {

                     i = j;

                     break;

                 }

             }

             if(j == len) break;

         }

     }

     for(i = ;i <= len;i ++)

     dp[i] = INF;

     str1 = ;end1 = ;

     str2 = ;end2 = ;

     que1[] = que2[] = ;

     for(i = ;i <= len;i ++)

     {

         dp[i] = dp[que1[str1]] + ;

         if(judge(str[i-]))

         {

             if(str2 < end2)

             dp[i] = min(dp[i],dp[que2[str2]]+);

         }

         else

         {

             str2 = end2 = ;

         }

         if(i == len) continue;

         while(str1 < end1&&dp[i] <= dp[que1[end1-]])

         end1 --;

         que1[end1++] = i;

         while(str1 < end1&&i - que1[str1] >= n)

         str1 ++;

         if(judge(str[i]))

         {

             while(str2 < end2&&dp[i] <= dp[que2[end2-]])

             end2 --;

             que2[end2++] = i;

             while(str2 < end2&&que2[str2] < pre[i])

             str2 ++;

             while(i - que2[str2] >= m&&str2 < end2)

             str2 ++;

         }

     }

     printf("%d\n",dp[len]);

     return ;

 }