#include<stdio.h>
#include<algorithm>
using namespace std;
long long int A[200100], B[200100], C[200100], D[200100];
int main(){
    long long int T, n, k, i, ans;
          scanf("%lld %lld", &n, &k);
        C[n+1]=D[n+1]=0;
        for(i=1;i<=n;i++){
        	scanf("%lld %lld", A+i, B+i);
		} 
        for(i=n;i>0;i--){
            C[i] = min(D[i+1],C[i+1])+A[i];
            D[i] = min(D[i+1],C[i+1])+B[i];
        }
        ans = C[1];
        for(i=2;i<=k;i++) ans = min(ans, C[i]);
        printf("%lld\n", ans);

}