#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
const int N = 1e6 + 10;
ll x[N], y[N];
int n, m;
ll ans, minx = 1e18;  

int main() {
	cin >> n >> m;
	for (int i = 1; i <= n; i++) {
		cin >> x[i] >> y[i];
	}
    for (int i = 1; i <= n; i++) {
        ans += (x[i] + y[i]);
        minx = min(minx, ans + (m - i) * y[i]);
    }
    cout << minx;
	return 0;
}

#include using namespace std; int main(){ long long n,m,s=0,mi=1e18; cin>>n>>m; int x[200008],y[2000008]; for(int i=0;i<n;i++){ cin>>x[i]>>y[i]; } for(int i=0;i<n;i++){ s+=x[i]+y[i]; mi=min(mi,s+(m-i-1)*y[i]); } cout<<mi; return 0; }

#include<bits/stdc++.h> using namespace std; long long a[1000010],b[1000010]; int main() { int n,m; cin>>n>>m; int x=min(n,m); for(int i=1;i<=n;i++)cin>>a[i]>>b[i]; long long minn=a[1]+b[1]m; long long sum=a[1]+b[1]; for(int i=2;i<=x;i++) { sum=sum+a[i]+b[i]; minn=min(minn,sum+b[i](m-2)); m--; } cout<<minn; return 0; }